Ischemic preconditioning and intermittent ischemia preserve bile flow in a rat model of ischemia reperfusion injury

Evidence that decreased expression of sinusoidal bile acid transporters accounts for the inhibition by rapamycin of bile flow recovery following liver ischemia

Rapamycin is employed as an immunosuppressant following organ transplant and, in patients with hepatocellular carcinoma, to inhibit cancer cell regrowth following liver surgery. Preconditioning the liver with rapamycin to induce the expression of antioxidant enzymes is a potential strategy to reduce ischemia reperfusion (IR) injury. However, pre-treatment with rapamycin inhibits bile flow, especially following ischemia. The aim was to investigate the mechanisms involved in this inhibition. In a rat model of segmental hepatic ischemia and reperfusion, acute administration of rapamycin by intravenous injection did not inhibit the basal rate of bile flow. Pre-treatment of rats with rapamycin for 24 h by intraperitoneal injection inhibited the expression of mRNA encoding the sinusoidal influx transporters Ntcp, Oatp1 and 2 and the canalicular efflux transporter Bsep, and increased expression of canalicular Mrp2. Dose-response curves for the actions of rapamycin on the expression of Bsep and Ntcp in cultured rat hepatocytes were biphasic, and monophasic for effects on Oatp1. In cultured tumorigenic H4IIE liver cells, several bile acid transporters were not expressed, or were expressed at very low levels compared to hepatocytes. In H4IIE cells, rapamycin increased expression of Ntcp, Oatp1 and Mrp2, but decreased expression of Oatp2. It is concluded that the inhibition of bile flow recovery following ischemia observed in rapamycin-treated livers is principally due to inhibition of the expression of sinusoidal bile acid transporters. Moreover, in tumorigenic liver tissue the contribution of tumorigenic hepatocytes to total liver bile flow is likely to be small and is unlikely to be greatly affected by rapamycin.

Intermittent ischemia enhances the uptake of indocyanine green to livers subject to ischemia and reperfusion

BACKGROUND AND AIM

Intermittent ischemia is known to promote post perfusion bile flow, and hence recovery of liver function following ischemia reperfusion of the liver. However, the mechanisms involved are not well understood. The aim of this study was to identify the step(s) in the bile acid transport pathway altered by intermittent ischemia.

METHODS

Arat model of segmental hepatic ischemia in which the bilateral median and left lateral lobes were made ischemic by clamping the blood vessels was used. Indocyanine green (ICG), infrared spectroscopy, and compartmental kinetic analysis, were used to indirectly monitor the movement of bile acids across hepatocytes in situ. Rates of bile flow were measured gravimetrically.

RESULTS

In control livers (not subjected to ischemia), the movement of ICG from the blood to bile fluid could be described by a three compartment model comprising the blood, a rapidly-exchangeable compartment, and the hepatocyte cytoplasmic space. In livers subjected to continuous clamping, the rates of ICG uptake to the liver, and outflow from the liver, were greatly reduced compared with those in control livers. Intermittent clamping (three episodes of 15 min clamping) compared with continuous clamping substantially increased the rate of ICG uptake from the blood but had less effect on the rate of ICG outflow from hepatocytes.

CONCLUSIONS

It is concluded that intermittent ischemia promotes post reperfusion bile flow in the early phase of ischemia reperfusion injury principally by enhancing the movement of bile acids from the blood to hepatocytes.

Ischemia/reperfusion injury after continuous or intermittent hepatic pedicle clamping in rabbits

BACKGROUND

The control of bleeding in hepatectomy is a challenge for surgeons. The hepatic pedicle clamping is a surgical maneuver that can provide reduction in bleeding, but it provokes a hepatocellular suffering. This, along with reperfusion after the clamping finishes, leads to an injury known as ischemia/reperfusion injury.

AIM

To examine the effects of the ischemia/reperfusion injury on the liver after continuous and intermittent hepatic pedicle clamping in an animal model, using the quantification of apoptosis for evaluation.

METHOD

Twenty New Zealand rabbits were assigned to groups 1 (control), 2 (60 minutes of continuous ischemia) and 3 (60 minutes of intermittent ischemia alternating 12 minutes of ischemia and three minutes of reperfusion). Liver biopsies were collected before ischemia, at its end and after six hours of reperfusion, when the animals were killed. The liver fragments were subjected to histological analysis (paraffinization and hematoxilin-eosin staining) and histochemical (Tunel reaction). Microscope fields of view were scanned for characterization and quantification of apoptosis.

RESULTS

Ischemia led to an increased apoptotic index in both experimental groups in comparison to controls, but similarly between them. After the reperfusion, the indexes returned to baseline values.

CONCLUSION

Clamping of the hepatic pedicle, either continuous or intermittent, induces apoptosis in liver cells in a similar way.

Topical hepatic hypothermia plus ischemic preconditioning: analysis of bile flow and ischemic injuries after initial reperfusion in rats

PURPOSE

To evaluate the effects of the topical liver hypothermia and IPC combination against I/R injury after initial reperfusion.

METHODS

In 32 Wistar rats, partial liver ischemia was induced for 90 minutes in normothermia (IN), ischemic preconditioning (IPC), 26ºC topical hypothermia (H) and 26ºC topical hypothermia plus IPC (H+IPC). MAP, body temperature and bile flow were recorded each 15 minutes. Plasmatic injury markers and tissue antioxidant defenses were assessed after 120 minutes of reperfusion.

RESULTS

MAP and body temperature remained constant during all experiment. Bile flow returned to levels similar to controls after 45 minutes of reperfusion in the H and H+IPC groups and increased significantly in comparison to the NI and IPC groups after 105 and 120 minutes. AST and ALT increased significantly in the normothermic groups in comparison to controls. TBARS levels decreased significantly in the H+IPC group in comparison to the other groups whereas Catalase levels increased significantly in the IPC group. SOD levels were significantly higher in the H group in comparison to all groups.

CONCLUSION

The induction of 26ºC topical hypothermia associated or not to IPC protected the ischemic liver against ischemia/reperfusion injuries and allowed an early recovery of the hepatic function.

Intermittent ischaemia maintains function after ischaemia reperfusion in steatotic livers

BACKGROUND

Ischaemic preconditioning (IPC) and intermittent ischaemia (INT) reduce liver injury after ischaemia reperfusion (IR). Steatotic livers are at a higher risk of IR injury, but the protection offered by IPC and INT is not well understood. The aim of the present study was to determine the effectiveness of IPC and INT in maintaining liver function in steatotic livers.

MATERIAL AND METHODS

A model of segmental hepatic ischaemia (45 min) and reperfusion (60 min) was employed using lean and obese Zucker rats. Bile flow recovery was measured to assess dynamic liver function, hepatocyte fat content quantified and blood electrolytes, metabolites and bile calcium measured to assess liver and whole body physiology. Liver marker enzymes and light and electron microscopy were employed to assess hepatocyte injury.

RESULTS

IPC was not effective in promoting bile flow recovery after IR in either lean or steatotic livers, whereas INT promoted good bile flow recovery in steatotic as well as lean livers. However, the bile flow recovery in steatotic livers was less than that in lean livers. In steatotic livers, ischaemia led to a rapid and substantial decrease in fat content. Steatotic livers were more susceptible to IR injury than lean livers, as indicated by increased blood ALT concentrations and major histological injury.

CONCLUSION

INT is more effective than IPC in restoring liver function in the acute phase of IR in steatotic livers. In obese patients, INT may be useful in promoting better liver function after IR after liver resection.

Ischemic preconditioning protects the pig liver by preserving the mitochondrial structure and downregulating caspase-3 activity

BACKGROUND DATA

The beneficial effects of ischemic preconditioning (IPC) on hepatic ischemia-reperfusion injury (I/RI) have been described. However, the way in which IPC causes the changes in mitochondrial ultrastructure seen in hepatic I/RI is not well understood.

OBJECTIVE

The objective of the present study was to determine whether IPC protects the liver from changes in mitochondrial structure and caspase 3 activity in the early phase of post-ischemic injury.

METHODS

A pig model consisting of 90 min of hepatic ischemia and 180 min of reperfusion was employed. Eighteen female pigs were randomly divided into three groups: sham-operated, non-preconditioned, and ischemic preconditioned (10 min ischemia followed by 10 min reperfusion). Serum concentrations of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and thiobarbituric acid reactive substances (TBARS), as well as bile flow, were measured. Liver biopsies were taken after reperfusion for histological, immunohistochemical (anti-caspase 3), and ultrastructural examinations.

RESULTS

The IPC procedure increased bile flow (p < 0.01), reduced serum AST level (p < 0.01), and reduced serum concentration of TBARS at 180 min of reperfusion (p = 0.05). Ischemic-preconditioned liver cells had less caspase 3 activity than the non-preconditioning group (p < 0.01), and changes in mitochondrial ultrastructure were reduced (p < 0.01).

CONCLUSION

IPC exerts a powerful protective effect against hepatic I/RI in the early phase of reperfusion, which may be mediated by preservation of mitochondrial structure and inhibition of caspase-3 activity.

Intermittent ischemia but not ischemic preconditioning is effective in restoring bile flow after ischemia reperfusion injury in the livers of aged rats

BACKGROUND/AIMS

Ischemic preconditioning (IPC) and intermittent ischemia (INT) reduce liver injury following ischemia reperfusion in liver resections. Aged livers are at higher risk for ischemia reperfusion injury, but little is known of the effectiveness of IPC and INT in aged livers. The aim of this study was to investigate the effects of IPC and INT on ischemia reperfusion injury in aged livers.

METHODS

A rat model of segmental hepatic ischemia (45 min) and reperfusion (60 min) was used. Bile flow, as an indicator of early hepatocyte damage and dynamic liver function, plasma concentrations of bilirubin, liver marker enzymes, and liver histology were assessed.

RESULTS

In young rats (8-13 weeks), IPC regimes of 10 min clamping and 10 min reperfusion, and 5 min clamping and 30 min reperfusion, restored bile flow to 23 and 42%, respectively, of the initial value, compared to 14 and 88% for continuous clamping and controls, respectively. An INT regime of three cycles of alternating 15 min perfusion and 15 min clamping gave a substantially greater (70%) restoration of bile flow. In aged rats (20-24 months), the IPC regimes did not give any restoration of bile flow. By contrast, the INT regime restored bile flow to 68%. Plasma bilirubin concentrations were lowest in the INT groups, whereas alanine transaminase concentrations for the IPC and INT groups compared with the continuous clamping groups showed no significant differences.

CONCLUSIONS

In young rats, INT is more effective than IPC in restoring the immediate consequences of IP-induced damage to hepatocytes and liver function after ischemia-reperfusion. In aged rats INT, but not IPC, reverses hepatocyte damage and restores liver function. INT may promote better hepatocyte and liver function than IPC following the surgical resection of aged livers.